The area is part of the overall heat transfer - the
UA. Effectiveness can also be stated in terms of UA,
and Cmin. To increase UA (and therefore
effectiveness) you can improve fin design, dimple
tubes to turbulate flow on the hot side (or increase
dimple death or play with the design of the dimples -
you want them in a helical pattern), or, as I was
telling a lister off line yesterday, tubes can be
finned internally (expensive and heavy). There is a
helluva lot to HX design, which is really my point -
don't just swap out parts ad hoc. Get some
information first.
--- Steven Fooshee <fooshst@stumail.gc.cc.fl.us>
wrote:
> Ron Soave wrote:
> >
> > The measure of how effective a heat exchanger is
> > called, you guessed it, effectiveness. What that
> is
> > is a ratio of how well the unit rejects heat
> divided
> > by how well it could theoretically reject heat:
> >
> > eff = (T_hot_in - T_hot_out)
> > ______________________
> > (T_hot_in - T_cold_in)
> >
>
> I've never worked with effectiveness measurements,
> but I do know that
> the total heat transfer in an exchanger is
> proportional to the surface
> area, the flow of the cooling medium, and the
> differential temperature
> across the exchanger. It seems to me that a radiator
> that restricts
> enough air flow to make a difference would have to
> make that difference
> up with the huge increase in surface area, or just
> not be a very good
> design. What was the change which you seem to have
> experience with?
> Good point about slowing down the flow. I've seen
> people try this and
> quickly get confused as to why it's suddenly rebuild
> time...
> --
>
>
> MCMLXIX Sprite: She needs a man with a slow hand.
> 1990 GS 500-E: She needs a lover with an easy touch.
> 1987 RX-7 TII: She needs somebody.... Oops,
> nevermind!
> "I don't like white people; they make too many
> generalizations."
>
> -
=====
Ron Soave
"I swear I found the key to the Universe in the engine of an old parked car." -
B. Springsteen
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